Today, computing devices such as personal computers, laptop computers, personal digital assistants, cell-phones, etc., are routinely used at work, home, and everywhere in-between. Computing devices advantageously enable the use of application specific software, file sharing, the creation of electronic documents, and electronic communication and commerce through the Internet and other computer networks. Typically, each computing device has a storage peripheral such as a disk drive.
A huge market exists for disk drives for mass-market computing devices such as desktop computers, laptop computers, as well as small form factor (SFF) disk drives for use in mobile computing devices (e.g., personal digital assistants (PDAs), cell-phones, digital cameras, etc.). To be competitive, a disk drive should be relatively inexpensive and provide substantial capacity, rapid access to data, and reliable performance.
Disk drives typically comprise a disk and a head connected to a distal end of an actuator arm which is rotated by a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk typically comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors typically comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the velocity of the actuator arm as it seeks from track to track.
Data is typically written to the disk by modulating a write current in an inductive coil of the head to record magnetic transitions onto the disk surface. During readback, the magnetic transitions are sensed by a read element (e.g., a magnetoresistive element) of the head and the resulting read signal is demodulated by a suitable read channel.
Also, a cache memory may temporarily store data to be written to the disk based upon write commands from the host computer. The cache memory is periodically flushed to write the data to the disk. However, when writing data to the disk, there may be an inherent performance degradation when dealing with unaligned writes on a disparate sector disk drive. This is because the data designated for writing may not completely fill a physical data sector of disk such that the missing data must be read from the disk before the physical data sector can be written to with the partial write data. This is sometimes referred to as a Read Modify Write (RMW). Unfortunately, because of the many unaligned writes that are necessary when flushing the cache, many RMW operations are required, resulting in an excessive amount of processing functions and time to implement all of the RMW operations.